To understand the characteristics of the water’s environmental carrying capacity in the Aiyi River in Yinchuan, Ninxia, China, a BP artificial neural network analysis based on water environmental factors and aquatic biodiversity metrics were conducted. Twelve indicators were used to construct an evaluation index system to examine the water environment carrying capacity of the river, namely ratio of water supply and water requirements; ratios of water environmental capacity to pollutant emissions of COD_Mn, BOD₅, TN, NH_3-N, and TP; self-purification rate; biodiversity indices of phytoplankton, zooplankton zoobenthos, and aquatic macrophytes; and a comprehensive nutrition state index. A model of water environmental carrying capacity was constructed according to the BP artificial neural network. The model, which quantitatively analyzed the water environmental carrying capacity of the Aiyi River, found it to be in the basic carrying state.